Acrolein is a valuable chemical compound useful in the manufacture of various useful unsaturated monomers and chemical intermediates including acrylic acid, acrylonitrile, glycerine and methionine. The principal process of manufacture is by the conversion of propylene by a partial oxidation reaction over a suitable catalyst. Some of the catalysts produce a mixture of acrolein and acrylic acid, while others are highly selective to either the aldehyde or acid. Representative of the former are: U.S. Pat. No. 3,755,434 to Celanese which employs a catalyst containing oxides of molybdenum, cobalt, tellurium and rhodium or boron; U.S. Pat. No. 3,829,476 to Mitsubishi Rayon Co., Ltd. which employs a catalyst containing phosphorus, tungsten, molybdenum, tellurium and combinations of nickel with either cobalt or iron, or cobalt and bismuth or iron and bismuth, and one of potassium or rubidium, all in combination with oxygen. Another patent, to Mitsubishi Rayon Co., Ltd. Japanese Pat. No. 4876804, employs the same combination except that potassium and rubidium are omitted and tin is added. This patent claims a 96% propylene conversion with yields of 85% to acrolein and 6% to acrylic acid.
Representative of the latter catalysts which are primarily selective to the aldehyde are: U.S. Pat. No. 3,755,458, which employs oxides of copper, arsenic, tellurium, and molybdenum or tungsten, and if tellurium is omitted molybdenum is chosen rather than tungsten; and German Pat. No. 2,334,037 to Daicel Ltd. which employs oxides of molybdenum, bismuth, iron, antimony and an alkali metal selected from potassium, rubidium and cesium.
Known catalysts closest to the present invention are disclosed in U.S. Pat. No. 3,855,308, which employs Co, Fe, Bi, W, Mo and Si, Tl and an alkali or alkaline earth metal; and U.S. Pat. No. 3,799,978, which employs Co, Fe, Bi, W, Mo, Si and an alkaline earth metal, both of which are assigned to Nippon Shokubai Kagaku Kogyo Co. Ltd. Another to Rohm & Haas Co., U.S. Pat. No. 3,786,000, employs Mo, Co, Fe, Bi and Sn and optionally one or more of Al, Ni, W, Cr, In and Nb.
Yet another catalyst used in making nitriles issued to Asahi Kasei Kogyo Kabushiki Kaisha (U.S. Pat. No. 3,766,092) employs Mo, Co, Fe, Bi, K and phosphorus. Certain claims of this patent exclude phosphorus as a catalyst component. Other references which employ Mo, Co, Fe, Bi plus at least one other metal which the catalyst of the present invention does not employ are U.S. Pat. Nos. 3,778,386 (Nippon Kayaku Co. Ltd.); 3,825,600 (Nippon Shokubai Kagaku Kogyo, Co. Ltd.); 3,825,502 (Nippon Kayaku Co. Ltd.); 3,761,424 (Deutsche Goldund Silber Scheide anstalt formals Roessler); while U.S. Pat. No. 3,894,091 (Daicel Ltd.) employs Mo, Fe, Bi, K and Sb.
The preparation of the oxidation catalysts employed in processes for making acrolein is generally known to the art and is accomplished by evaporating to dryness either aqueous solutions or suspensions of the salts of the metal components of the catalyst. This may be done in the presence of a support for the catalyst so that the catalytic components are deposited on a carrier or, if unsupported, the resulting solids may be pulverized and subsequently pelleted by compression. A thick slurry or paste of the catalytic components may also be extruded and cut into pellet form. Finally, the supported and unsupported catalytic components are calcined at from about 300.degree. C to 600.degree. C (preferably about 500.degree. C) to form the oxides which are the catalytic components employed in the process. The original componds of the metals are unimportant so long as they form the desired oxides upon calcination. Sometimes the original metal compounds are of such nature that their solutions will co-precipitate, which precipitate is then washed and calcined.
Other methods could be employed such as co-gelling the various ingredients and thereafter drying the gelled mass in a conventional manner; or the solution or gel may be spray dried to form a particulate material which is subsequently compressed into suitable forms or used as is if the particle size is suitable for a fluid bed reactor.